Photosensitive Polyimide gives near vertical side walls with normal exposure and development. If that is not the right angle image reversal allows control of the side wall angle from a normal side wall through vertical to an acute overhang. All with smooth side walls and controllable angle. Bill Moffat, CEO Yield Engineering Systems, Inc. 203-A Lawrence Drive, Livermore, CA 94551-5152 (925) 373-8353 www.yieldengineering.com -----Original Message----- From: mems-talk-bounces+bmoffat=yieldengineering.com@memsnet.org [mailto:mems- talk-bounces+bmoffat=yieldengineering.com@memsnet.org] On Behalf Of Pramod Gupta Sent: Thursday, July 22, 2010 10:07 AM To: General MEMS discussion Subject: Re: [mems-talk] rib waveguide using dry etch Are you trying to etch polymer to make waveguide? If yes, you can try low pressure/high power process to get vertical wall. But this process also increases the sidewall roughness. So you have to compromise between your etched wall angle and side wall roughness. You canmix O2 intoyour SF6 + C4F8chemistry. Good luck. With regards, Pramod Gupta